• Brazil is trying to crack down on near-slave labor conditions that have helped keep down the cost of ethanol production.

• Paramilitary groups are forcing peasants from their land in Colombia to make room for palm oil plantations, raising the specter of "blood biofuels."

The dark side of biofuels could potentially overshadow their positive effects, said Raya Widenoja, biofuels researcher with the Worldwatch Institute, an environmental group. Benefits include cooling an overheating climate and boosting developing economies.

"Biofuels do have the potential to herald in a brighter, more sustainable future — if they are developed wisely," she said.

Widenoja and others worry the biofuels backlash could threaten that future if public outcry persuades politicians to cut research money or projects. Funding is critical to develop the next generation of biofuels. Ethanol from sources other than corn and soybeans could address some of the negative aspects, Widenoja said.

"It would be rather unfortunate if the public stopped supporting anything to do with biofuels. It would mean we lose the chance to develop high potential and sustainable energy sources," she said.

The problems aren't limited to Third World nations. Corn ethanol production requires the burning of fossil fuels, and threatens water quality and availability, according to a new study by the National Academy of Sciences.

"What we do here triggers impacts around the world," including raising the price of grain, said Chad Hart, an agriculture economist at Iowa State University.

Widenoja said biofuels have intensified agricultural methods that rely on a single crop and damage the environment through fertilizer and pesticide use. These practices also perpetuate "social injustices that tend to keep rural areas poor, agricultural laborers exploited and poor migrants flooding to cities in search of a better life," she said.

"But these are all typical agriculture/commodity industry problems. ... Biofuel producers and consumers haven't invented them, they just haven't solved them," she said.

For example, the demand for palm and other vegetable oils has damaged rainforests and other areas, Hart said. But biofuels are only one factor in that demand. China, India and other rapidly growing nations are consuming more vegetable oils in their diets, he said.

Hart and Widenoja agreed that governments, biofuels producers and others can foster better, more sustainable biofuels by encouraging:

New feedstocks: Most ethanol is made from two crops: corn and sugarcane. Most biodiesel is made from soy or palm oil. Scientists are studying the energy potential for plant life not considered a crop, such as algae.

New fuels: Other biofuels may hold greater promise than ethanol. DuPont and BP plan to produce butanol from sugar beets in Great Britain. The fuel can be transported by pipeline — reducing energy consumption — and can offer better fuel economy than ethanol, the companies say.

"I hope people don't get hung up on ethanol and think that's the only biofuel you can create," Hart said.

"The great thing about cellulosic ethanol is that it can be developed so that land will remain valuable and farmers can profit from growing food or fuel — and the fuel sources can be grown in a much more sustainable way than the food crops have been grown traditionally," Widenoja said.

Subsistence farmers would increase incomes and improve farming practices, she said, and land- and labor-rich developing countries could export biofuels and boost economies.